Antischistosomal drugs and other chemotherapeutic agents are attracting wide concern because of their potential carcinogenic and mutagenic hazards to treated individuals in human populations. Our previous studies have shown that many antischistosomal agents are mutagenic Neurospora crassa and that there is no correlation between mutagenicity and antischistosomal activity of antischistosomal agents. Studies have extended to other chemotherapuetic agents, and to determine whether antischistosomal agents and other chemotherapeutic agents induce particular types of genetic alterations in N. crassa. Genetic analysis of mutants induced by niridazole and metronidazole indicate that niridazole induces predominantly base-pair substitution mutations. None of the niridazole-induced mutants resulted from multilocus deletions. The spectrum of genetic alterations induced by metronidazole is similar to that induced by monofunctional alkylating agents.